58 lines
2.0 KiB
OCaml
58 lines
2.0 KiB
OCaml
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let read name =
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let ic = open_in name in
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let try_read () =
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try Some (input_line ic)
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with End_of_file -> None in
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let rec loop acc =
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match try_read () with
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| Some s -> loop (s::acc)
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| None -> close_in ic; acc in
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List.rev (loop [])
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let build lines =
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let rec aux res idx = function
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| h :: t -> let [instr; value] = String.split_on_char ' ' h in
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let () = res.(idx) <- (0, instr, int_of_string value) in
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aux res (idx + 1) t
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| [] -> res in
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aux (Array.make (List.length lines) (0, "nop", 0)) 0 lines
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let rec step pc acc instructions =
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let (n, instr, v) = instructions.(pc) in
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let () = instructions.(pc) <- (n + 1, instr, v) in
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match instr with
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| "nop" -> (n + 1, pc + 1, acc)
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| "acc" -> (n + 1, pc + 1, acc + v)
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| "jmp" -> step (pc + v) acc instructions
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| _ -> raise (Failure "unreachable")
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let run instructions =
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let rec aux pc acc instructions =
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match step pc acc instructions with
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| (2, _, _) -> raise (Failure (Printf.sprintf "Loop detected with accumulator %d!" acc))
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| (_, pc, result) when pc = (Array.length instructions - 1) -> result
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| (_, pc, acc_) -> aux pc acc_ instructions
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in aux 0 0 instructions
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let rec swap_from idx ins =
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match ins.(idx) with
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| (_, "nop", v) when v <> 0 -> let () = ins.(idx) <- (0, "jmp", v) in (idx + 1, ins)
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| (_, "jmp", v) -> let () = ins.(idx) <- (0, "nop", v) in (idx + 1, ins)
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| _ -> swap_from (idx + 1) ins
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let fix instructions =
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let rec aux idx ins instructions =
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try run ins
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with e -> let (i, ins) = swap_from idx (Array.copy instructions) in
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aux i ins instructions
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in aux 0 (Array.copy instructions) instructions
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let () = try let _ = read "day8.input" |> build |> run in ()
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with Failure msg -> print_endline msg
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let () = print_endline (string_of_int (read "day8.input" |> build |> fix))
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